Solid-state imaging element and driving method therefor, and electronic apparatus

ABSTRACT

The present technology relates to a solid-state imaging element, a driving method therefor, and an electronic apparatus, by which the characteristics of phase-difference pixels can be made constant irrespective of a chip position. 
     In a pixel array section, a normal pixel including a photodiode (PD) that receives and photoelectrically converts incident light such that a color component signal is obtained, and a phase-difference pixel including a pair of a photodiode (PD 1 ) and a photodiode (PD 2 ) including light-receiving surfaces having a size depending on an image height such that a phase difference detection signal is obtained are arranged in a matrix form. The pair of the photodiode (PD 1 ) and the photodiode (PD 2 ) each include a first region serving as a charge accumulation main part and a second region that performs photoelectric conversion and contributes to charge transfer to the main part. The present technology is applicable to a CMOS image sensor, for example.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/587,035, filed May 4, 2017, which is a continuation of U.S. patentapplication Ser. No. 15/022,478, filed Mar. 16, 2016, which claims thebenefit of PCT Application No. PCT/JP2014/074245 having an internationalfiling date of Sep. 12, 2014, which designated the United States, whichPCT application claimed the benefit of Japanese Patent Application No.2013-197872 filed Sep. 25, 2013, the disclosures of which areincorporated herein by reference in their entirety.

TECHNICAL FIELD

The present technology relates to a solid-state imaging element, adriving method therefor, and an electronic apparatus and moreparticularly to a solid-state imaging element, a driving methodtherefor, and an electronic apparatus, by which the characteristics ofphase-difference pixels can be made constant irrespective of a chipposition.

BACKGROUND ART

Conventionally, solid-state imaging elements such as a CMOS(Complementary Metal Oxide Semiconductor) image sensor have been widelyused for imaging apparatuses. The imaging apparatus of this type has anAF (Autofocus) function of automating focusing. In recent years,requirements for AF accuracy and AF speed of a subject are increasedmore and more.

For example, in general, an AF module is additionally incorporated in adigital single-lens reflex camera. It involves an increase in casingsize and mounting cost. Therefore, some of mirrorlessinterchangeable-lens cameras and compact digital still cameras realizethe AF function by contrast AF without the additionally incorporated AFmodule. However, it is difficult to say that the AF speed is sufficientin current state.

Therefore, a digital camera that increases the AF speed by incorporatingphase-difference pixels in a solid-state imaging element and realizingthe AF function by image surface phase difference AF has been inpractical use. In general, in the image surface phase difference method,a phase-difference pixel A and a phase-difference pixel B are paired forrealizing the AF function. As a method of improving the AF accuracy, itis effective to increase the number of phase-difference pixels that areincorporated in the solid-state imaging element. Conventionally, it isrealized by setting the phase-difference pixels A and B to be the samesize as a normal pixel for imaging and, for example, changing a metallight shield.

Furthermore, Patent Document 1 discloses a technology in whichphase-difference pixels A and B are placed in one pixel for increasingthe number of pixels for AF, to thereby improve the AF accuracy. Inaddition, Patent Document 2 discloses a technology relating to back sideillumination type phase-difference pixels.

Patent Document 1: Japanese Patent Application Laid-open No. 2012-165070

Patent Document 2: Japanese Patent Application Laid-open No. 2012-84816

SUMMARY OF INVENTION Problem to be Solved by the Invention

Patent Document 1 discloses the image surface phase difference AF usinga PD division system. This is a method in which phase-difference pixelsA and B are placed in one pixel. In this method, a light-collecting spotS is set in a boundary between the phase-difference pixel A and thephase-difference pixel B.

For example, in a lens interchangeable digital camera, thelight-collecting spot position depends on the F-value of theinterchangeable lens. Even if the lenses are not interchanged, theF-value is changed when wide-angle imaging and telephoto and zooming areperformed, and the light-collecting spot position is correspondinglychanged. In general, regarding the image surface phase difference AFusing the PD division system, the light-collecting spot S is not changedin the center portion of an angle of view (center portion of chip) inany lens. Therefore, if the phase-difference pixel A and thephase-difference pixel B are set to have the same size, it is possibleto set the light-collecting spot S in the boundary between thephase-difference pixel A and the phase-difference pixel B. FIG. 1 showsan example in which the light-collecting spot S is set in the center ofa pixel.

On the other hand, in a peripheral portion of the angle of view(peripheral portion of chip), the light-collecting spot S can be set inthe center of the pixel in some lenses if a microlens is subjected topupil correction. However, if lenses having different F-values are used,there is a possibility that the light-collecting spot S may be deviatedfrom the center of the pixel. In this case, in order to set thelight-collecting spot S in the boundary between the phase-differencepixel A and the phase-difference pixel B, it is necessary to set thelight-receiving surfaces of the phase-difference pixel A and thephase-difference pixel B to have a different size. The light-collectingspot position is changed depending on an image height, and hence it isnecessary to change, depending on the arrangement position of the pixelsin the solid-state imaging element, the size ratio between thephase-difference pixels A and B in that pixel. FIG. 2 shows an examplein which the size of the phase-difference pixel A is set to be smallerthan the size of the phase-difference pixel B. By changing the ratiobetween the phase-difference pixels A and B in this manner, it ispossible to set the light-collecting spot S in the boundary between thephase-difference pixel A and the phase-difference pixel B.

However, as shown in FIG. 2, when the size ratio between thephase-difference pixels A and B is changed, the charge accumulationregion of the phase-difference pixel A becomes smaller than the chargeaccumulation region of the phase-difference pixel B. Thus, thesaturation signal amount of the phase-difference pixel A decreases.Furthermore, the size of the phase-difference pixels A and B isvariously changed depending on the position of the light-collecting spotS. Therefore, it is not easy to completely transfer charges of all thephase-difference pixels A and B.

Note that Patent Document 2 discloses the technology relating to theback side illumination type phase-difference pixels and it does notadopt the PD division system.

The present technology has been made in view of such situations to makethe characteristics of the phase-difference pixels constant irrespectiveof a chip position such as the center portion of an angle of view and aperipheral portion of the angle of view.

Means for Solving the Problem

A solid-state imaging element according to an aspect of the presenttechnology includes: a pixel array section in which a first pixelincluding a photoelectric conversion unit that receives andphotoelectrically converts incident light such that a color componentsignal is obtained, and a second pixel including a pair of a firstphotoelectric conversion unit and a second photoelectric conversion unitincluding light-receiving surfaces having a size depending on an imageheight such that a phase difference detection signal is obtained arearranged in a matrix form, the pair of the first photoelectricconversion unit and the second photoelectric conversion unit eachincluding a first region serving as a charge accumulation main part, anda second region that performs photoelectric conversion and contributesto charge transfer to the main part.

In the pair of the first photoelectric conversion unit and the secondphotoelectric conversion unit, the second regions on a light incidentside have a size depending on pupil correction and the first regions onan opposite side of the light incident side have the same size.

Impurity concentration in the first region is higher than impurityconcentration in the second region.

The second region is larger than the first region.

It further includes: a first transfer transistor that transfers chargesaccumulated in the first photoelectric conversion unit, and a secondtransfer transistor that transfers charges accumulated in the secondphotoelectric conversion unit, in which in the pair of the firstphotoelectric conversion unit and the second photoelectric conversionunit, impurity concentration in a region near the first transfertransistor and a region near the second transfer transistor is higherthan impurity concentration in other regions.

The first transfer transistor is disposed near a position closest to acenter of the light-receiving surface of the first photoelectricconversion unit, and the second transfer transistor is disposed near aposition closest to a center of the light-receiving surface of thesecond photoelectric conversion unit.

It further includes: a first floating diffusion region held for readingout a charge transferred from the first photoelectric conversion unit bythe first transfer transistor, as a signal; and a second floatingdiffusion region held for reading out a charge transferred from thesecond photoelectric conversion unit by the second transfer transistor,as a signal.

Exposure and transfer in the first photoelectric conversion unit and thesecond photoelectric conversion unit are performed at the same time.

The pair of the first photoelectric conversion unit and the secondphotoelectric conversion unit includes a separation section therebetweenthat is continuously changed.

The pair of the first photoelectric conversion unit and the secondphotoelectric conversion unit is separated by metal, an oxide film, orimpurities.

In the solid-state imaging element according to the aspect of thepresent technology, the first pixel including the photoelectricconversion unit that receives and photoelectrically converts incidentlight such that the color component signal is obtained, and the secondpixel including the pair of a the first photoelectric conversion unitand the second photoelectric conversion unit including thelight-receiving surfaces having a size depending on the image heightsuch that the phase difference detection signal is obtained are arrangedin a matrix form in the pixel array section. The pair of the firstphotoelectric conversion unit and the second photoelectric conversionunit each include the first region serving as the charge accumulationmain part, and the second region that performs photoelectric conversionand contributes to charge transfer to the main part.

A driving method for a solid-state imaging element, according to anaspect of the present technology, the solid-state imaging elementincluding a pixel array section in which a first pixel including aphotoelectric conversion unit that receives and photoelectricallyconverts incident light such that a color component signal is obtained,and a second pixel including a pair of a first photoelectric conversionunit and a second photoelectric conversion unit includinglight-receiving surfaces having a size depending on an image height suchthat a phase difference detection signal is obtained are arranged in amatrix form, the pair of the first photoelectric conversion unit and thesecond photoelectric conversion unit each including a first regionserving as a charge accumulation main part, and a second region thatperforms photoelectric conversion and contributes to charge transfer tothe main part, the method including: a step of separately driving, bythe pixel driving unit, the pair of the first photoelectric conversionunit and the second photoelectric conversion unit to perform exposureand transfer in the first photoelectric conversion unit and the secondphotoelectric conversion unit at the same time.

In the driving method according to the aspect of the present technology,the pair of the first photoelectric conversion unit and the secondphotoelectric conversion unit including the light-receiving surfaceshaving a size depending on the image height is separately driven toperform exposure and transfer in the first photoelectric conversion unitand the second photoelectric conversion unit at the same time.

An electronic apparatus according to an aspect of the present technologyincludes: a solid-state imaging element, including a pixel array sectionin which a first pixel including a photoelectric conversion unit thatreceives and photoelectrically converts incident light such that a colorcomponent signal is obtained, and a second pixel including a pair of afirst photoelectric conversion unit and a second photoelectricconversion unit including light-receiving surfaces having a sizedepending on an image height such that a phase difference detectionsignal is obtained are arranged in a matrix form, the pair of the firstphotoelectric conversion unit and the second photoelectric conversionunit each including a first region serving as a charge accumulation mainpart, and a second region that performs photoelectric conversion andcontributes to charge transfer to the main part; and a control unit thatcontrols image surface phase difference AF (Autofocus) using the phasedifference detection signal output from the solid-state imaging element.

In the electronic apparatus according to the aspect of the presenttechnology, the image surface phase difference AF is controlled usingthe phase difference detection signal output from the solid-stateimaging element.

Effects of the Invention

According to an aspect of the present technology, it is possible to makethe characteristics of the phase-difference pixels constant irrespectiveof a chip position.

BRIEF DESCRIPTION OF DRAWINGS

[FIG. 1] A diagram for describing a PD division system.

[FIG. 2] A diagram for describing the PD division system.

[FIG. 3] A block diagram showing a configuration of an embodiment of asolid-state imaging element to which the present technology is applied.

[FIG. 4] A diagram showing an arrangement example of phase-differencepixels in a pixel array section.

[FIG. 5] A plane view showing a configuration of a unit pixel in thecenter portion of an angle of view.

[FIG. 6] A plane view showing a configuration of a unit pixel in aperipheral portion of the angle of view.

[FIG. 7] A sectional view showing a configuration of a unit pixel in thecenter portion of an angle of view in the case where a first pupilcorrection method is adopted.

[FIG. 8] A sectional view showing a configuration of a unit pixel in aperipheral portion of the angle of view in the case where the firstpupil correction method is adopted.

[FIG. 9] A plane view showing a configuration of a unit pixel in thecenter portion of the angle of view in the case where a second pupilcorrection method is adopted.

[FIG. 10] A plane view showing a configuration of a unit pixel in theperipheral portion of the angle of view in the case where the secondpupil correction method is adopted.

[FIG. 11] A block diagram showing a configuration of an embodiment of anelectronic apparatus to which the present technology is applied.

MODE(S) FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments according to the present technology will bedescribed with reference to the drawings.

<Configuration Example of Solid-State Imaging Element>

FIG. 3 is a block diagram showing a configuration of an embodiment of asolid-state imaging element to which the present technology is applied.

A CMOS image sensor 100 is an example of the solid-state imagingelement. As shown in FIG. 3, the CMOS image sensor 100 is configured toinclude a pixel array section 111 and a peripheral circuit section. Theperipheral circuit section is constituted of a vertical driving unit112, a column processing unit 113, a horizontal driving unit 114, and asystem control unit 115.

The CMOS image sensor 100 further includes a signal processing unit 118and a data storage unit 119. The signal processing unit 118 and the datastorage unit 119 may be placed on the same semiconductor substrate asthe CMOS image sensor 100 or may be an external signal processing unitprovided in a semiconductor substrate other than the CMOS image sensor100, for example, a DSP (Digital Signal Processor) or processing bysoftware.

In the pixel array section 111, unit pixels (hereinafter, also simplyreferred to as “pixels”) are arranged in a two-dimensional matrix form.Note that a specific configuration of the unit pixel will be describedlater. In the pixel array section 111, pixel driving lines 116 arefurther formed in left and right directions of the figure for each rowwith respect to the matrix-form pixel arrangement and vertical signallines 117 are formed in upper and lower directions of the figure foreach column. One ends of the pixel driving lines 116 are connected tooutput ends corresponding to the rows of the vertical driving unit 112.

The vertical driving unit 112 is a pixel driving unit that isconstituted of a shift resistor, an address decoder, or the like anddrives the pixels of the pixel array section 111, for example, at thesame time or for each row. The signals output from the unit pixels inthe pixel row that is selectively scanned by the vertical driving unit112 are supplied to the column processing unit 113 through therespective vertical signal lines 117. For each of the pixel columns ofthe pixel array section 111, the column processing unit 113 performspredetermined signal processing on signals output from the pixels in theselected row through the vertical signal lines 117 and temporarilyretains the pixel signals after signal processing.

Specifically, the column processing unit 113 performs at least noiseelimination, for example, CDS (Correlated Double Sampling) as signalprocessing. Due to the CDS by the column processing unit 113,fixed-pattern noise specific to the pixel, for example, reset noise orvariations in threshold of an amplification transistor is eliminated.The column processing unit 113 may be set to have, for example, an A/D(Analog/Digital) conversion function for outputting a signal level as adigital signal other than the noise elimination processing.

The horizontal driving unit 114 is constituted of the shift resistor,the address decoder, and the like and sequentially selects unit circuitscorresponding to the pixel columns of the column processing unit 113. Byselective scanning by the horizontal driving unit 114, the pixel signalssubjected to signal processing by the column processing unit 113 aresequentially output.

The system control unit 115 includes a timing generator that generatesvarious timing signals and performs driving control on the verticaldriving unit 112, the column processing unit 113, the horizontal drivingunit 114, the data storage unit 119, and the like based on the varioustiming signals generated by the timing generator.

The signal processing unit 118 has at least an addition processingfunction and performs various types of signal processing such asaddition processing on the pixel signals output from the columnprocessing unit 113. For signal processing in the signal processing unit118, the data storage unit 119 temporarily stores data necessary for theprocessing.

Note that the CMOS image sensor 100 is a back side illumination typeimage sensor that reads out, from the front side of the semiconductorsubstrate, a signal depending on charges generated in the photoelectricconversion unit due to light entering the photoelectric conversion unitin the semiconductor substrate from the back side of the semiconductorsubstrate.

<Structure of Unit Pixel>

Next, with reference to FIGS. 4 to 6, a specific structure of unitpixels arranged in a matrix form in the pixel array section 111 of FIG.3 will be described. The unit pixels include normal pixels 120 foroutputting color component signals for forming an image signalindicating an image of the subject as pixel signals and aphase-difference pixel 121 for outputting a phase difference detectionsignal used for the image surface phase difference AF as a pixel signal.

FIG. 4 shows phase-difference pixels 121 arranged in a row out of theunit pixels arranged in the pixel array section 111. As shown in FIG. 4,the phase-difference pixels 121 have the same size light-receivingsurfaces in the center portion of an angle of view (center portion ofchip) that is on an axis. Meanwhile, in peripheral portions of the angleof view (peripheral portion of chip) outside the axis, they havedifferent size light-receiving surfaces depending on the image height.For example, in the case of the example of FIG. 4, the phase-differencepixel 121 located on the left side in the figure includes a smallerlight-receiving surface of the phase-difference pixel 121A. Meanwhile,the phase-difference pixel 121 located on the right side of the figureincludes a smaller light-receiving surface of a phase-difference pixel121B.

FIGS. 5 and 6 are plane views each showing a configuration of a unitpixel. FIG. 5 shows the configuration of the unit pixel in the centerportion of the angle of view. FIG. 6 shows the configuration of the unitpixel in the peripheral portion of the angle of view.

The normal pixel 120 is constituted of a photodiode (PD) serving as thephotoelectric conversion unit and a plurality of pixel transistors. Thephotodiode (PD) includes a region for receiving and photoelectricallyconverting incident light and accumulating signal charges generated bythe photoelectric conversion. For example, the photodiode (PD) is aburied type photodiode that is formed by forming, with respect to aP-type well layer formed on an N-type substrate, a P-type layer on thefront side of the substrate and burying an N-type buried layer.

Furthermore, a plurality of pixel transistors include four transistorsof a transfer transistor (TR), a reset transistor (RST), anamplification reset transistor (AMP), and a selection transistor (SEL).The transfer transistor (TR) is a transistor for reading out chargesaccumulated in the photodiode (PD) to a floating diffusion region (FD)region. The reset transistor (RST) is a transistor for setting thepotential of the floating diffusion region (FD) to a specific value. Theamplification reset transistor (AMP) is a transistor for electricallyamplifying signal charges read out by the floating diffusion region(FD). The selection transistor (SEL) is a transistor for selecting onepixel row and reading out pixel signals to the vertical signal lines117.

A capacitance-switching transistor (FDG) is a transistor for switchingconversion efficiency in the floating diffusion region (FD).Furthermore, an overflow control transistor (OFG) is a transistor forrealizing overflow control.

As described above, the normal pixels 120 includes the photodiode (PD)and the plurality of pixel transistors and outputs color componentsignals of any one of red (R), green (G), and blue (B), for example aspixel signals. Although a Gb-pixel, a Gr-pixel, and an R-pixel are shownas the normal pixels 120 in FIG. 5, a B-pixel also has the sameconfiguration as the pixels corresponding to the other color components.

The phase-difference pixel 121 adopts a PD division system. Instead ofone photodiode (PD) serving as the photoelectric conversion unit, thephase-difference pixel 121 includes two photodiodes (PD1, PD2) asobtained by halving it. Note that, also in the following description,out of the pair of phase-difference pixels in the phase-difference pixel121, one pixel constituted of a photodiode (PD1) and a plurality ofpixel transistors will be referred to as the phase-difference pixel 121Aand the other pixel constituted of a photodiode (PD2) and a plurality ofpixel transistors will be referred to as the phase-difference pixel121B. That is, regarding the phase-difference pixel 121, by forming thetwo photodiodes (PD1, PD2) in this pixel, the phase-difference pixel121A and the phase-difference pixel 121B are configured as a pair.

In the phase-difference pixel 121A, the photodiode (PD1) has a regionfor receiving and photoelectrically converting incident light andaccumulating signal charges generated by the photoelectric conversion.For example, the photodiode (PD1) is formed as the buried typephotodiode as in the photodiode (PD) of the normal pixels 120.Furthermore, the plurality of pixel transistors include four transistorsof the transfer transistor (TR1), the reset transistor (RST1), theamplification reset transistor (AMP1), and the selection transistor(SEL1) as in the normal pixels 120.

Furthermore, in the phase-difference pixel 121B, the photodiode (PD2)has a region for receiving and photoelectrically converting incidentlight and accumulating signals charges generated by the photoelectricconversion. For example, the photodiode (PD2) is formed as the buriedtype photodiode as in the photodiode (PD) of the normal pixels 120.Furthermore, the plurality of pixel transistors include, as in thenormal pixels 120, four transistors of the transfer transistor (TR2),the reset transistor (RST2), the amplification reset transistor (AMP2),and the selection transistor (SEL2).

That is, in the phase-difference pixel 121, the pixel transistors (TR1,RST1, AMP1, SEL1) for the photodiode (PD1) and the pixel transistors(TR2, RST2, AMP2, SEL2) for the photodiode (PD2) are separatelyprovided, and hence exposure and transfer in the photodiode (PD1) andthe photodiode (PD2) can be performed at the same time.

Here, FIG. 5 shows a configuration of the unit pixel in the centerportion of the angle of view. Therefore, the photodiode (PD1) in thephase-difference pixel 121A and the photodiode (PD2) in thephase-difference pixel 121B have the same size light-receiving surfaces.On the other hand, as shown in FIG. 6, although the phase-differencepixel 121 in the peripheral portion of the angle of view is configuredsuch that the phase-difference pixel 121A and the phase-difference pixel121B are paired as in the phase-difference pixel 121 in the centerportion of the angle of view, the size of the light-receiving surface ischanged depending on the image height. Specifically, the size of thelight-receiving surface of the photodiode (PD1) in the phase-differencepixel 121A is smaller than the size of the light-receiving surface ofthe photodiode (PD2) in the phase-difference pixel 121B.

In this manner, by changing the size of the light-receiving surfacedepending on the image height, the light-collecting spot S is set in theboundary between the phase-difference pixel 121A and thephase-difference pixel 121B. However, along with it, the chargeaccumulation region of the phase-difference pixel 121A becomes smallerthan the charge accumulation region of the phase-difference pixel 121Bwith the result that the saturation signal amount of thephase-difference pixel 121A is lowered as described above. Furthermore,as described above, the sizes of the phase-difference pixel 121A and thephase-difference pixel 121B are variously changed depending on theposition of the light-collecting spot S. Therefore, it is not easy tocompletely transfer the charges of all the phase-difference pixels 121Aand 121B.

In view of this, hereinafter, a first pupil correction method and asecond pupil correction method for suppressing a reduction in thesaturation signal amount of the phase-difference pixels 121A and 121Band completely transferring the charges of the phase-difference pixels121A and 121B in the case where the size of the light-receiving surfaceis changed depending on the image height will be described.

First Embodiment

First, with reference to FIGS. 7 and 8, the first pupil correctionmethod as the first embodiment will be described. FIG. 7 shows asectional view of the normal pixel 120 (Gb-pixel) and thephase-difference pixel 121 in the center portion of the angle of viewshown in FIG. 5. FIG. 8 shows a sectional view of the normal pixel 120(Gb-pixel) and the phase-difference pixel 121 in the peripheral portionof the angle of view shown in FIG. 6.

As shown in FIG. 7, in the first pupil correction method, the photodiode(PD1) in the phase-difference pixel 121A is formed of a first region R1serving as a charge accumulation main part and a second region R2 thatperforms photoelectric conversion and contributes to charge transfer tothe main part. Furthermore, the photodiode (PD2) in the phase-differencepixel 121B is also formed of the first region R1 and the second regionR2. Note that, in each of the photodiodes (PD1, PD2), the impurityconcentration is represented by gradation and the impurity concentrationin the first region R1 is higher than the impurity concentration in thesecond region R2. Furthermore, occupying rate of the second region R2 inthe whole region is higher than that of the first region R1.

Furthermore, the phase-difference pixel 121 changes the size of thelight-receiving surface depending on the image height. Therefore, it isunnecessary to change the width of the second region R2 on lightincident side (back side) in the center portion of the angle of viewwhile it is necessary to reduce the width of the second region R2 in theperipheral portion of the angle of view. That is, as shown in FIG. 8, inthe peripheral portion of the angle of view, the width of the secondregion R2 of the photodiode (PD1) in the phase-difference pixel 121A isformed to be narrower than the width of the second region R2 of thephotodiode (PD2) in the phase-difference pixel 121B. On the other hand,regarding light incident side and opposite side (front side), the widthof the first region R1 of the photodiode (PD1) and the width of thefirst region R1 of the photodiode (PD2) are formed to be equal in theperipheral portion of the angle of view as in the center portion of theangle of view.

That is, element separation portions serving to separate the elements ofthe pixels are separately formed as an element separation portion 151 onthe back side and an element separation portion 152 on the front side.The element separation portion 151 changes the width of the secondregion R2 between the center portion of the angle of view and theperipheral portion of the angle of view. On the other hand, the elementseparation portion 152 sets the width of the first region R1 to be equalbetween the center portion of the angle of view and the peripheralportion of the angle of view. With this, in each phase-difference pixel121, even if the size of the light-receiving surface is continuouslychanged depending on the image height and the size of the second regionR2 on the back side is changed, the size of the first region R1 on thefront side is not changed. As a result, the size of the first region R1having a high impurity concentration is fixed. Therefore, in theperipheral portion of the angle of view, in comparison with the centerportion of the angle of view, a large difference does not occur betweenthe saturation signal amount and the transfer ease. Thus, it is possibleto make the characteristics of the phase-difference pixels 121 arrangedin the pixel array section 111 constant.

Note that the element separation portion 151 and the element separationportion 152 can be formed of, for example, metal, an oxide film, orimpurities.

As described above, in the first pupil correction method, regarding thephase-difference pixel 121A and the phase-difference pixel 121B, thefirst regions R1 and the second regions R2 have the same configurationsin the center portion of the angle of view of FIG. 7 and the secondregions R2 have different configurations while the first regions R1 havethe same configurations in the peripheral portion of the angle of viewof FIG. 8. In this manner, a large difference is prevented fromoccurring between the saturation signal amount and the transfer ease,and the characteristics of the phase-difference pixels 121 arranged inthe pixel array section 111 are made constant.

Second Embodiment

Next, with reference to FIGS. 9 and 10, the second pupil correctionmethod as a second embodiment will be described. FIG. 9 shows a planeview of the normal pixel 120 (Gb-pixel) and the phase-difference pixel121 in the center portion of the angle of view shown in FIG. 5. FIG. 10shows a plane view of the normal pixel 120 (Gb-pixel) and thephase-difference pixel 121 in the peripheral portion of the angle ofview shown in FIG. 6.

As shown in FIG. 9, in the second pupil correction method, as in thefirst pupil correction method, the photodiode (PD1) in thephase-difference pixel 121A is formed of a first region R1 serving as acharge accumulation main part and a second region R2 that performsphotoelectric conversion and contributes to charge transfer to the mainpart. Furthermore, the photodiode (PD2) in the phase-difference pixel121B is also formed of the first region R1 and the second region R2.Note that, in FIGS. 9 and 10, the impurity concentration in thephotodiodes (PD1, PD2) is represented by gradation as in FIGS. 7 and 8.

Furthermore, in the phase-difference pixel 121A, a transfer transistor(TR1) is disposed in parallel to a direction in which thephase-difference pixel 121A and the phase-difference pixel 121B aredivided, and near the position closest to the center of thelight-receiving surface of the photodiode (PD1). With this, the impurityconcentration in a region near the transfer transistor (TR1) becomeshigher than the impurity concentration in other regions. Similarly, inthe phase-difference pixel 121B, a transfer transistor (TR2) is disposedin parallel to a direction in which the phase-difference pixel 121A andthe phase-difference pixel 121B are divided, and near the positionclosest to the center of the light-receiving surface of the photodiode(PD2). With this, the impurity concentration in a region near thetransfer transistor (TR2) becomes higher than the impurity concentrationin other regions.

Furthermore, the phase-difference pixel 121 changes the size of thelight-receiving surface depending on the image height. Therefore, it isunnecessary to change the size of the light-receiving surface in thecenter portion of the angle of view while it is necessary to reduce thesize of the light-receiving surface in the peripheral portion of theangle of view. That is, as shown in FIG. 10, in the peripheral portionof the angle of view, the size of the light-receiving surface in thephase-difference pixel 121A is formed to be smaller than the size of thelight-receiving surface in the phase-difference pixel 121B. However, inthe peripheral portion of the angle of view, transfer transistors (TR1,TR2) are arranged in the peripheral portion of the angle of view as inthe center portion of the angle of view, and hence the impurityconcentration in regions near the transfer transistors (TR1, TR2) ishigher than the impurity concentration in other regions.

That is, in each phase-difference pixel 121, even if the size of thelight-receiving surface is continuously changed depending on the imageheight and the size of the light-receiving surface in, for example, thephase-difference pixel 121A becomes small, the first region R1 having ahigh impurity concentration is constantly formed in a region near thetransfer transistor (TR1). As a result, the first region R1 having ahigh impurity concentration is not influenced by the change in size.Therefore, in the peripheral portion of the angle of view, in comparisonwith the center portion of the angle of view, a large difference doesnot occur between the saturation signal amount and the transfer ease.Thus, it is possible to make the characteristics of the phase-differencepixels 121 arranged in the pixel array section 111 constant.

As described above, in the second pupil correction method, although thesize of the light-receiving surface is changed in the center portion ofthe angle of view of FIG. 9 and the peripheral portion of the angle ofview of FIG. 10, the structures near the transfer transistors (TR1, TR2)have the same configurations and the impurity concentration in theregions near the transfer transistors (TR1, TR2) is higher than that inthe other regions. In this manner, a large difference is prevented fromoccurring between the saturation signal amount and the transfer ease,and the characteristics of the phase-difference pixels 121 arranged inthe pixel array section 111 are made constant.

As described above, according to the present technology, in thephase-difference pixels 121 arranged in the pixel array section 111,when continuously changing the size of the light-receiving surfacedepending on the image height, the first region R1 having a highimpurity concentration is not influenced by the change. Therefore, inthe peripheral portion of the angle of view, in comparison with thecenter portion of the angle of view, a large difference does not occurbetween the saturation signal amount and the transfer ease. Thus, it ispossible to make the characteristics of the phase-difference pixels 121constant. That is, in the phase-difference pixels 121, the main parts ofthe charge accumulation have the same structure, and hence it becomespossible to perform pupil correction and suppress a reduction of thesaturation signal amount at the same time and to similarly performcharge transfer.

Furthermore, regarding the phase-difference pixel 121, thephase-difference pixel 121A and the phase-difference pixel 121B areinstalled as a pair in one pixel. Therefore, it is possible to easilyincrease the number of the phase-difference pixels 121 arranged in thepixel array section 111 and enhance the characteristics of thephase-difference pixels 121. Furthermore, the size of thephase-difference pixels 121A and 121B is changed depending on the imageheight depending on lens pupil correction. As a result, it is possibleto increase an interchangeable lens that can cope with the image surfacephase difference AF.

Note that, although the phase-difference pixels 121 are arranged in eachrow in the pixel array section 111 have been described above, thepresent technology is also applicable to the case where thephase-difference pixels 121 are arranged in each column. Also in thiscase, the phase-difference pixels 121A and 121B include the same sizelight-receiving surfaces in the center portion of the angle of view.However, the size of the light-receiving surfaces is changed dependingon the image height in the peripheral portion of the angle of view.Specifically, for example, each phase-difference pixel 121 is configuredto include the size of the light-receiving surface in a state in whichthe plurality of phase-difference pixels 121 arranged in the row shownin FIG. 4 are rotated by 90 degrees in a counterclockwise directionaround the phase-difference pixel 121 in the center portion of the angleof view.

Furthermore, the present technology is not limited to application to thesolid-state imaging element. That is, the present technology isapplicable to general electronic apparatuses using a solid-state imagingelement for an image capturing section (photoelectric conversion unit),for example, an imaging apparatus such as a digital camera, a portableterminal apparatus having an imaging function, or a copying machineusing a solid-state imaging element for an image read-out section.Furthermore, the solid-state imaging element may be formed as one chipor may be in the form of a module having an imaging function in which animaging section and a signal processing unit or an optical system arepacked together.

<Configuration Example of Electronic Apparatus to Which PresentTechnology is Applied>

FIG. 11 is a block diagram showing a configuration of an embodiment ofthe electronic apparatus to which the present technology is applied.

As shown in FIG. 11, an imaging apparatus 300 serving as the electronicapparatus includes an optical unit 301 that is formed of a lens group, asolid-state imaging element 302 that adopts the configurations of theabove-mentioned unit pixels 120, and a DSP (Digital Signal Processor)circuit 303 that is a camera signal processing circuit. Furthermore, theimaging apparatus 300 also includes a frame memory 304, a display unit305, a recording unit 306, an operation unit 307, a power-supply unit308, and a control unit 309. The DSP circuit 303, the frame memory 304,the display unit 305, the recording unit 306, the operation unit 307,the power-supply unit 308, and the control unit 309 are connected to oneanother via a bus line 310.

The optical unit 301 captures incident light (image light) from asubject and forms an image thereof on an imaging surface of thesolid-state imaging element 302. The solid-state imaging element 302converts the light amount of the incident light, whose image is formedon the imaging surface by the optical unit 301, into an electricalsignal for each pixel and outputs color component signals for formingimage signals showing the image of the subject as pixel signals.Furthermore, the solid-state imaging element 302 outputs phasedifference detection signals used for image surface phase difference AFas pixel signals. As this solid-state imaging element 302, thesolid-state imaging element such as the CMOS image sensor 100 accordingto the above-mentioned embodiment, that is, the solid-state imagingelement that is capable of making the characteristics of thephase-difference pixels 121 arranged in the pixel array section 111constant can be used.

The display unit 305 is constituted of a panel type display apparatussuch as a liquid-crystal display panel and an organic EL (ElectroLuminescence) panel. The display unit 305 displays a still image ormoving image that is captured by the solid-state imaging element 302.The recording unit 306 records the moving image or still image capturedby the solid-state imaging element 302 on a recording medium such as aflash memory.

The operation unit 307 issues operation commands relating to the variousfunctions of the imaging apparatus 300 according to user's operations.The power-supply unit 308 appropriately supplies various powers asoperation power sources to the DSP circuit 303, the frame memory 304,the display unit 305, the recording unit 306, the operation unit 307,and the control unit 309 as those supply targets.

The control unit 309 controls operations of the respective sections ofthe imaging apparatus 300. Furthermore, the control unit 309 calculatesa defocus amount by performing predetermined calculation using the phasedifference detection signal from the solid-state imaging element 302 andcontrols driving of imaging lens and the like of the optical unit 301such that focusing is achieved depending on this defocus amount. Withthis, the image surface phase difference AF is performed and focus isachieved on the subject.

Note that, in the above-mentioned embodiment, the description has beenmade exemplifying the case where the present technology is applied tothe CMOS image sensor in which the unit pixels that detect signalcharges corresponding to the light amounts of the visible light asphysical amounts are arranged in a matrix form. However, the presenttechnology is not limited to application to the CMOS image sensor and isapplicable to general solid-state imaging elements using a column systemin which a column processing unit is disposed in each pixel column of apixel array section.

Furthermore, the present technology is not limited to application to thesolid-state imaging element that detects a distribution of incidentlight amounts of visible light and captures it as an image and isapplicable to general solid-state imaging elements (physical amountdistribution apparatuses) such as a solid-state imaging element thatcaptures a distribution of incident amounts of infrared rays, X-rays,particles, or the like as an image and a fingerprint sensor that detectsa distribution of other physical amounts such as a pressure and anelectrostatic capacity in a broad sense and captures it as an image.

Note that embodiments of the present technology are not limited to theabove-mentioned embodiments and various modifications can be madewithout departing from the gist of the present technology.

The present technology may also take the following configurations.

(1)

A solid-state imaging element, including:

a pixel array section in which

-   -   a first pixel including a photoelectric conversion unit that        receives and photoelectrically converts incident light such that        a color component signal is obtained, and    -   a second pixel including a pair of a first photoelectric        conversion unit and a second photoelectric conversion unit        including light-receiving surfaces having a size depending on an        image height such that a phase difference detection signal is        obtained are arranged in a matrix form, the pair of the first        photoelectric conversion unit and the second photoelectric        conversion unit each including    -   a first region serving as a charge accumulation main part, and    -   a second region that performs photoelectric conversion and        contributes to charge transfer to the main part.

(2)

The solid-state imaging element according to (1), in which

in the pair of the first photoelectric conversion unit and the secondphotoelectric conversion unit, the second regions on a light incidentside have a size depending on pupil correction and the first regions onan opposite side of the light incident side have the same size.

(3)

The solid-state imaging element according to (2), in which

impurity concentration in the first region is higher than impurityconcentration in the second region.

(4)

The solid-state imaging element according to (3), in which

the second region is larger than the first region.

(5)

The solid-state imaging element according to (1), further including:

a first transfer transistor that transfers charges accumulated in thefirst photoelectric conversion unit, and

a second transfer transistor that transfers charges accumulated in thesecond photoelectric conversion unit, in which

in the pair of the first photoelectric conversion unit and the secondphotoelectric conversion unit, impurity concentration in a region nearthe first transfer transistor and a region near the second transfertransistor is higher than impurity concentration in other regions.

(6)

The solid-state imaging element according to (5), in which

the first transfer transistor is disposed near a position closest to acenter of the light-receiving surface of the first photoelectricconversion unit, and

the second transfer transistor is disposed near a position closest to acenter of the light-receiving surface of the second photoelectricconversion unit.

(7)

The solid-state imaging element according to (6), further including:

a first floating diffusion region held for reading out a chargetransferred from the first photoelectric conversion unit by the firsttransfer transistor, as a signal; and

a second floating diffusion region held for reading out a chargetransferred from the second photoelectric conversion unit by the secondtransfer transistor, as a signal.

(8)

The solid-state imaging element according to any one of (1) to (7), inwhich

exposure and transfer in the first photoelectric conversion unit and thesecond photoelectric conversion unit are performed at the same time.

(9)

The solid-state imaging element according to any one of (1) to (8), inwhich

the pair of the first photoelectric conversion unit and the secondphotoelectric conversion unit includes a separation section therebetweenthat is continuously changed.

(10)

The solid-state imaging element according to any one of (1) to (9), inwhich

the pair of the first photoelectric conversion unit and the secondphotoelectric conversion unit is separated by metal, an oxide film, orimpurities.

(11)

A driving method for a solid-state imaging element, including

-   -   a pixel array section in which        -   a first pixel including a photoelectric conversion unit that            receives and photoelectrically converts incident light such            that a color component signal is obtained, and        -   a second pixel including a pair of a first photoelectric            conversion unit and a second photoelectric conversion unit            including light-receiving surfaces having a size depending            on an image height such that a phase difference detection            signal is obtained are arranged in a matrix form, the pair            of the first photoelectric conversion unit and the second            photoelectric conversion unit each including        -   a first region serving as a charge accumulation main part,            and        -   a second region that performs photoelectric conversion and            contributes to charge transfer to the main part, the method            including:    -   a step of separately driving, by the pixel driving unit, the        pair of the first photoelectric conversion unit and the second        photoelectric conversion unit to perform exposure and transfer        in the first photoelectric conversion unit and the second        photoelectric conversion unit at the same time.

(12)

An electronic apparatus, including:

a solid-state imaging element, including

-   -   a pixel array section in which        -   a first pixel including a photoelectric conversion unit that            receives and photoelectrically converts incident light such            that a color component signal is obtained, and        -   a second pixel including a pair of a first photoelectric            conversion unit and a second photoelectric conversion unit            including light-receiving surfaces having a size depending            on an image height such that a phase difference detection            signal is obtained are arranged in a matrix form, the pair            of the first photoelectric conversion unit and the second            photoelectric conversion unit each including        -   a first region serving as a charge accumulation main part,            and        -   a second region that performs photoelectric conversion and            contributes to charge transfer to the main part; and

a control unit that controls image surface phase difference AF(Autofocus) using the phase difference detection signal output from thesolid-state imaging element.

DESCRIPTION OF SYMBOLS

-   100 CMOS image sensor-   111 pixel array section-   120 normal pixel-   121, 121A, 121B phase-difference pixel-   151, 152 element separation portion-   300 imaging apparatus-   302 solid-state imaging element-   309 control unit-   R1 first region-   R2 second region-   PD, PD1, PD2 photodiode-   TR, TR1, TR2 transfer transistor-   RST, RST1, RST2 reset transistor-   AMP, AMP1, AMP2 amplification reset transistor-   SEL, SEL1, SEL2 selection transistor-   FDG, FDG1, FDG2 capacitance-switching transistor

What is claimed is:
 1. An imaging device, comprising: a pixel arraysection including a first pixel arranged at a center portion of thepixel array section and a second pixel arranged at a peripheral portionoutside of the center portion, each of the first pixel and the secondpixel including: a first photoelectric converter and a secondphotoelectric converter, each of the first photoelectric converter andthe second photoelectric converter having a first region and a secondregion, wherein a front side of each of the first and the second pixelsis divided into respective first regions of the first and the secondphotoelectric converters by a first element isolation region, wherein aback side of each of the first and the second pixels is divided intorespective second regions of the first and the second photoelectricconverters by a second element isolation region, the back side receivinglight and being opposite to the front side, wherein, in a crosssectional view, a width of the second region of the first photoelectricconverter of the first pixel is greater than a width of the secondregion of the first photoelectric converter of the second pixel, andwherein, in the cross sectional view, a width of the second region ofthe second photoelectric converter of the first pixel is less than awidth of the second region of the second photoelectric converter of thesecond pixel.
 2. The imaging device according to claim 1, wherein, inthe cross sectional view, a width of the first region of the firstphotoelectric converter of the first pixel is substantially similar to awidth of the first region of the second photoelectric converter of thefirst pixel.
 3. The imaging device according to claim 1, wherein animpurity concentration of the first region is higher than an impurityconcentration of the second region.
 4. The imaging device according toclaim 1, wherein a pair of the first photoelectric converter and thesecond photoelectric converter is utilized for generating a phasedifference detection signal.
 5. The imaging device according to claim 1,wherein at least one of the first and second element isolation regionscomprise an impurity.
 6. The imaging device according to claim 5,wherein at least one of the first and second element isolation regionscomprise an oxide film.
 7. The imaging device according to claim 1,wherein the first photoelectric converter is disposed at a peripheralside of the second photoelectric converter of the second pixel.
 8. Theimaging device according to claim 1, wherein, in the cross sectionalview, the width of the second region of the first photoelectricconverter of the first pixel is substantially similar to a width of thefirst region of the first photoelectric converter of the first pixel. 9.The imaging device according to claim 1, wherein, in the cross sectionalview, the width of the second region of the second photoelectricconverter of the first pixel is substantially similar to a width of thefirst region of the second photoelectric converter of the first pixel.10. The imaging device according to claim 1, wherein, in the crosssectional view, the width of the second region of the firstphotoelectric converter of the second pixel is less than a width of thefirst region of the first photoelectric converter of the second pixel.11. The imaging device according to claim 1, wherein, in the crosssectional view, the width of the second region of the secondphotoelectric converter of the second pixel is greater than a width ofthe first region of the second photoelectric converter of the secondpixel.
 12. The imaging device according to claim 1, wherein, in thecross sectional view, a width of the first region of the firstphotoelectric converter of the second pixel is substantially similar toa width of the first region of the second photoelectric converter of thesecond pixel.
 13. The imaging device according to claim 1, wherein, inthe cross sectional view, the width of the second region of the firstphotoelectric converter of the first pixel is substantially similar tothe width of the second region of the second photoelectric converter ofthe first pixel.
 14. The imaging device according to claim 1, wherein,in the cross sectional view, the width of the second region of the firstphotoelectric converter of the second pixel is different from the widthof the second region of the second photoelectric converter of the secondpixel.
 15. The imaging device according to claim 1, wherein, in thecross sectional view, the width of the second region of the firstphotoelectric converter of the second pixel is less than the width ofthe second region of the second photoelectric converter of the secondpixel.
 16. An imaging device, comprising: a pixel array sectionincluding a first pixel arranged at a center portion of the pixel arraysection and a second pixel arranged at a peripheral portion outside ofthe center portion, each of the first pixel and the second pixelincluding: a first photoelectric converter and a second photoelectricconverter, each of the first photoelectric converter and the secondphotoelectric converter having a first region and a second region,wherein the first region of the first photoelectric converter isdisposed between a first front side element separation portion and asecond front side element separation portion, wherein the first regionof the second photoelectric converter is disposed between a third frontside element separation portion and the second front side elementseparation portion, wherein the second region of the first photoelectricconverter is disposed between a first back side element separationportion and a second back side element separation portion, wherein thesecond region of the second photoelectric converter is disposed betweena third back side element separation portion and the second back sideelement separation portion, wherein a distance between the first backside element separation portion of the first pixel and the second backside element separation portion of the first pixel is greater than adistance between the first back side element separation portion of thesecond pixel and the second back side element separation portion of thesecond pixel in a cross sectional view, wherein a distance between thesecond back side element separation portion of the first pixel and thethird back side element separation portion of the first pixel is lessthan a distance between the second back side element separation portionof the second pixel and the third back side element separation portionof the second pixel in the cross sectional view, wherein a distancebetween the first back side element separation portion of the secondpixel and the second back side element separation portion of the secondpixel is less than a distance between the first front side elementseparation portion of the second pixel and the second front side elementseparation portion of the second pixel in the cross sectional view, andwherein a distance between the second back side element separationportion of the second pixel and the third back side element separationportion of the second pixel is greater than a distance between thesecond front side element separation portion of the second pixel and thethird front side element separation portion of the second pixel in thecross sectional view.